This section introduces aspects that may be helpful to facilitating a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
It is expected that future optical networks will employ coherent polarization-multiplex quadrature phase-shift-keying (PM-QPSK) transmission format for efficient use of spectral bandwidth. Such formats will most likely be used in long-haul and ultra-long-haul (LH/ULH) dense wavelength-division multiplexing (DWDM) systems. Furthermore, to overcome the bottleneck in transponder interface rates, next-generation coherent receivers are expected to employ multi-wavelength reception to increase the degree of optical parallelism, hence increasing system capacity. This increased capacity does, however, typically require more complex receiver frontends.